I think dogs, amongst other animals, have a sensitivity to oncoming disaster that humans do not posses. Animals sensing storms, hurricanes, earthquakes, has all been well-documented.
I am amazed at the 'cancer-sniffing' dogs. These special animals can indeed sense illness in their masters, but can't always communicate it without the proper training.
http://news.nationalgeographic.com/news/2004/08/0820_040820_detectordogs.html
Given this evidence, I do believe that dogs and other pets do indeed sense these things, including the impending death of a master or mistress.
I have type II diabetes, with liver complications. The doctors don't know which came first, to be honest. My dog chooses to sleep close to my abdomen, or on my pillows, where my scent is noticed by him. I'm not dying by any means, but his natural empathy is a constant source of encouragement. Good dog....